02 sensor acting up = MILs?

[Sith]

My back 02 sensors are acting up (CEL comes off and on) and since I have a bassani xpipe ( epper: )planned for the future my question is should I simply buy MILs now? will it shut the CEL off?

If that didn't make sense, what I'm trying to do is fix my 02 sensors but since I'll be getting a xpipe shortly it's probably a waste of money to buy new 02 sensors and put them in, correct?

 

[LAXbronco65]

i just recently pulled my BBK Xpipe off and put the stocker back on so i can smog and sell my cobra. so i have a pair of steeda plug and play MILS ill sell ya. PM me if your interested.

 

[scotty98]

I have a bbk o/r h and dallas mustang mills and i think one is bad cause my light comes on and off. get the mills that will keep the cel off i just have a bad one ond havent replaced it yet. :dw:

 

[Sith]

another thing, I'm confused about something. With the CEL on from an 02 sensor the car runs lean right? (obviously effecting performance..) But if I were to shut the 02 sensor off via MILs, would the car be running normal again?

 

[SVT Lurch]

I thought it ran rich with the CEL on, I usually get worse gas mileage whenever mine is on. That held true on 2 96 GTs, this 97 Cobra, and an 00 L.

 

[Sith]

I thought it ran rich with the CEL on, I usually get worse gas mileage whenever mine is on. That held true on 2 96 GTs, this 97 Cobra, and an 00 L.

you're right, it's rich sorry. But will it be normal again even if i shut it off via Mils? and if so, why is that?

 

[STAMPEDE3]

The rears have nothing to do with the A/F ratio, only the fronts.
The rear O2s only tell the computer if your cats are working properly which is why the CEL comes on with the cats removed.

Mils don't always work, they only amplify the rear O2 signal to adjust the reading so the computer thinks the cats are still there.
If a rear O2 sensor is bad and reading out of range the Mil can only compensate so much and the reading will still be out of range and the CEL will still be on.
Best bet is a chip to turn the rear off.

 

[CY98Cobra]

Anytime the CEL is on the cars goes into "limp mode". The car will run rich and timing will be pulled. I also have a CEL for the rear o2 even with my mil eliminators. It kills performance and gas mileage. I'm going to switch the eliminators from one side to the other to see if it is an o2 sensor or the eliminator.

 

[STAMPEDE3]

The rears have nothing to do with A/F. The computer is smart enough to know what is throwing the CEL.
When I had my tune done, with the CEL on for the rear O2s the car was lean as hell. we added 30% fuel across the board to get it safe.
Turning the rear O2s off made NO difference.
That limp mode is a myth. The car knows what is important to go into limp mode.
Not just any CEL will put it in limp mode, and it knows what ones.

 

[CY98Cobra]

Funny how when the cel is on I can't spin the tires from a second gear punch and when the light is off I can from any rpm. Also funny how my gas mileage has dropped off to about 15mpg since it has been on, when it was 19-20 before. That only leaves the o2 since I can shut it off with my scanner, go out and notice and immediate increase in performance, then when it comes back on it feels like a dog.

My computer must be dumber than yours cause it is definitely in "limp mode".

 

[STAMPEDE3]

I ran with the CEL on for the rears and then turned it off with the chip while data logging. It makes NO difference if it is indeed the REAR O2s throwing the code.
15MPG or miles per tank? if it is MPG then,
You have something else wrong!

 

[STAMPEDE3]

Funny how when the cel is on I can't spin the tires from a second gear punch and when the light is off I can from any rpm. Also funny how my gas mileage has dropped off to about 15mpg since it has been on, when it was 19-20 before. That only leaves the o2 since I can shut it off with my scanner, go out and notice and immediate increase in performance, then when it comes back on it feels like a dog.

My computer must be dumber than yours cause it is definitely in "limp mode".

I just re-read this and You have something wrong. It is in limp mode but I can garrentee you it is not the Rear O2s doing it.

Before my tune, I ran 3 years with the CEL on for the rear O2s and still got 20MPG AVG. with the 4.30 gears.All my track passes were the same as with it off, the car never went into limp mode. You must have an underlying problem.

 

[DKS2814V]

My CEL is always on, I had the codes run and it says that my left bank is running lean, something like. The other is this pesky Purge Valve Solenoid that I can't find anywhere on the firewall.... Is it behind the wheel?! What the fu?

I get about 22 to 24 on the highway with my 4.10's..... Great gas mileage I would have to say for high horsepower car. My car doesn't seem to be in "limp" mode.... Definitely roasts the tires all the way to third gear.... I ran a 13.6 spinning all three gears into fourth with my check engine light on....

Can someone verify that this "limp" mode deal is true?
Another thing, where the hell is this Purge Valve Solenoid and Sensor....

 

[Sith]

Is it worth it to me to get MILs now (before the o/r pipe) in order to shut the 02 sensors off, or am I going to need to replace the sensor? I'm getting mixed signals.

 

[STAMPEDE3]

Limp mode is real, certain codes put it into limp mode. The O2s are not one of them.

On rear O2s and Mils.
The rear O2 is there to tell if the Cats are working properly. That is their only purpose. This is why you remove the cats the CEL comes on. However with that said let me explain the best I can as how they work.
For this example I will use round numbers to make it easy to understand. with the first number being the only accurate one.


The rear O2 with a good sensor and properly working cat sends a 400Ma signal to the computer.
When you remove the cat that signal drops to 200Ma and is now out of range so the CEL comes on.
Mils simply amplify the 200Ma signal by adding another 200Ma so the computer sees 400Ma and turns the CEL off.
However, If your rear O2 sensor is BAD and reading low say 100Ma then the Mil will add 200Ma and the computer will only see 300Ma and still be out of range. CEL stays on.

This is why some people say my CEL is still on with Mils.
You must still maintain good O2s for them to work and still it is a hit or miss kind of thing.
I went with a tune. You can completly turn off the rears and then garrenteed no CEL from the rears.

 

[STAMPEDE3]

One other thing, with not Cats, the rear will be very dependent on the fronts, If the car is running rich or lean due to the fronts it will affect the rear also. Remember the cat's are no longer there to burn up the excess.

 

[CY98Cobra]

I just re-read this and You have something wrong. It is in limp mode but I can garrentee you it is not the Rear O2s doing it.

Before my tune, I ran 3 years with the CEL on for the rear O2s and still got 20MPG AVG. with the 4.30 gears.All my track passes were the same as with it off, the car never went into limp mode. You must have an underlying problem.

There is nothing else wrong. I have scanned the car with two different scanners and it says rear o2 sensor circuit malfunction (or somethng like that). I will clear it and then go drive it. The car is immediately more powerful then before the code was cleared. When the CEL comes back on (usually the next time I drive the car) the car is weaker than before. Not to say it falls on its face, it will still give a good push in the backside, but not near what it was before. I have done this numerous times (clearing the code and driving) and it's the same every time. The computer has to be pulling timing and dumping fuel based on performance and the decrease in gas mileage because the car runs great when I clear the code.

I'm changing the tranny fluid soon and will fool with it then to see if it's the mil eliminator or the o2 sensor.

 

[SVT Lurch]

you're right, it's rich sorry. But will it be normal again even if i shut it off via Mils? and if so, why is that?

I was jsut making sure I'm not crazy, :beer:

 

[Sith]

So you're saying it's a hit or miss trying to shut the CEL off via MILs?

 

[SVT Lurch]

Basically. Unless you get the computer scanned and find out exactly the code that tripped the light.